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Overview

Radio components such as modulators, demodulators and tuners are traditionally implemented in hardware components. The advent of modern computing and analogue to digital converters allows most of these traditionally hardware based components to be implemented into software instead. Hence, the term software defined radio. This enables easy signal processing and thus cheap wide band scanner radios to be produced. (quoted from https://www.rtl-sdr.com/about-rtl-sdr/)

An good (though not the latest) introduction on the SDR is available here. A list of SDR can be found here

Hardware

There are many SDR platforms available on the market, with different specifications and prices. A comprehensive list can be found at here

A comparison between different SDR is produced by LimeSDR and quoted here. Source: https://www.crowdsupply.com/lime-micro/limesdr-mini#comparison-table

ItemHackRF OneEttus B200Ettus B210BladeRF x40RTL-SDRLimeSDRLimeSDR Mini
Frequency Range1 MHz - 6 GHz70 MHz - 6 GHz70 MHz - 6 GHz300 MHz - 3.8 GHz22 MHz - 2.2 GHz100 kHz - 3.8 GHz10 MHz - 3.5 GHz
RF Bandwidth20 MHz61.44 MHz61.44 MHz40 MHz3.2 MHz61.44 MHz30.72 MHz
Sample Depth8 bit12 bit12 bit12 bit8 bit12 bit12 bit
Sample Rate20 MSPS61.44 MSPS61.44 MSPS40 MSPS3.2 MSPS61.44 MSPS30.72MSPS
TX Channels1121021
RX Channels1121121
DuplexHalfFullFullFullN/AFullFull
InterfaceUSB 2.0USB 3.0USB 3.0USB 3.0USB 2.0USB 3.0USB 3.0
Programmable Logic Gates64 macrocell CPLD75k100k40k (115k avail)N/A40k16K
Open SourceFullSchematic, FirmwareSchematic, FirmwareSchematic, FirmwareNoFullFull
Oscillator Precision+/- 20 ppm+/- 2 ppm+/- 2 ppm+/- 1 ppm?+/-1 ppm initial, +/-4 ppm stable+/- 1 ppm initial, +/- 4 ppm stable
Transmit Power-10 dBm+ (15 dBm @ 2.4 GHz)10 dBm+10 dBm+6 dBmN/Amax 10 dBm (depending on freq.)max 10 dBm (depending on freq.)
Price$299$686$1,119$420~$10$299\$159

USRP has different series, including network series, bus series, embedded series. A selection guide is given in https://kb.ettus.com/Selecting_an_USRP_Device

Some USRP series do not have RF capabilities, e.g., the N210 USRP. A separate RF daughterboard will be required.

Wireless Open Access Research Platform (WARP)

Strictly speaking, WARP is not an SDR platform, because it uses a WiFi chipset MAX2829. There are two reference designs, namely 802.11 reference design and WARPLab reference design. The driver has been developed for both designs and the users can simply focus on developing their applications and prototypes.

• WARP 802.11 reference design is compatible with the commercial WiFi standard. The PHY and MAC codes are running at the FPGA. An experimental framework has been developed with two WARP boards connecting to a PC via a Ethernet switch. Python has been used. A more detailed introduction can be found at link
• WARPLab reference design is very suitable for fast prototype of physical layer algorithm. Two or more WARP boards are connected to a PC via a Ethernet switch. The signal is modulated at the Matlab, then transferred to WARP transmitter via Ethernet cable. The data is triggered for transmission through the real wireless channel. The WARP receiver captures the signal and transfer it to the PC/Matlab via Ethernet cable for further processing.